1. Field of the Invention
The present invention relates to a luminescent display in which an organic electroluminescent (organic EL) element is preferably used as a luminescent element, and also to a method of producing it.
2. Description of the Related Art
Conventionally, an organic EL element is known which is enabled to luminesce by causing a current to flow through a phosphor member formed on a glass plate or a translucent organic film.
FIG. 4 diagrammatically shows a sectional structure of a luminescent display in which an organic EL element is used as a luminescent element. As shown in FIG. 4, the luminescent display of the conventional art is configured by sequentially stacking a transparent electrode (layer) 302, an organic layer 303, and a metal electrode (layer) 304 on a transparent substrate 301.
Usually, an organic EL element is seemed to be a capacitive luminescent element which is equivalently expressed by a circuit resistance component, a capacitance component, and a luminescence component. When a voltage is applied across the transparent electrode 302 and the metal electrode 304, therefore, charges corresponding to the electric capacitance of the element flow into the electrodes as a displacement current to be accumulated therein. When the voltage exceeds a fixed level (barrier voltage), a current flows into the organic layer 303 configured by an organic EL element, via the electrodes 302 and 304, and luminescence is started in proportion to the current.
FIG. 5 shows an example of an arrangement of transparent electrodes and metal electrodes in a luminescent display of simple matrix driving.
As shown in FIG. 5, a luminescent display in which the above-mentioned organic EL element is used as a luminescent element is formed by, on a transparent glass substrate 101, sequentially stacking: plural parallel stripe-like transparent electrodes 102 which are made of ITO or the like and arranged at predetermined intervals; a luminescent portion 103 configured by an organic layer; and plural parallel stripe-like metal electrodes 104 which are perpendicular to the transparent electrodes 102 and arranged at predetermined intervals. In order to attain moisture proofing, a protective film which is not shown is formed over the whole face of the substrate 101 on which the metal electrodes 104 and the organic layer 103 are formed.
In the luminescent display, formed are luminescent pixels each configured by setting, as one unit, one of regions of the organic layer 103 where paired ones of the transparent electrodes 102 and the metal electrodes 104 intersect and face each other with interposing the respective regions. A required number of the pixels are arranged into a matrix form, thereby forming a luminescent display of simple matrix driving.
In the thus formed luminescent display, a driving source which scan-drives the transparent electrodes 102 and the metal electrodes 104 adequately applies a voltage across the transparent electrode 102 and the metal electrode 104 that correspond to an appropriate pixel, and a current flows through the organic layer 103 of the corresponding pixel, so that light is emitted.
In production of such a luminescent display, the possibility of occurrence of a damage or deposition of particles is higher as the area of the display screen is larger. This is a great factor of a reduced yield in the production.
When a flaw 10 is produced in the transparent electrode 302 or a particle 20 is deposited onto the transparent electrode 302 as shown in FIG. 4, the organic layer 303 is insufficiently grown in the corresponding portion of the surface of the transparent electrode 302. A defect 30 may be caused in the organic layer 303 by any reason.
As a result, in the part where the organic layer 303 is insufficiently grown, the metal electrode layer 304 may be directly grown on the transparent electrode layer 302, so that the transparent electrode layer 302 serving as an anode may be short-circuited with the metal electrode layer 304 serving as a cathode.
Even when such a defect does not result in a short circuit, the organic layer 303 between the transparent electrode 302 and the metal electrode 304 is grown so as to be very thin, and the current for luminescence is concentrated into the thinned part. As a result, the current hardly flows through the peripheral region of the part, thereby producing a problem in that the pixel fails to luminesce. This problem is the greatest factor of a failure in production, and largely lowers the production yield.
Therefore, a countermeasure such as that a substrate is elaborately washed has been taken. However, such washing requires much labor. Furthermore, it is impossible to completely eliminate particles or flaws in the transparent electrode 302, or irregularity of the surface of the transparent electrode 302 by washing.
As described above, in a luminescent display in which an organic EL element is used as a luminescent element, when a concave flaw exists or dust is deposited onto the transparent electrode 302, the film growth is insufficiently performed in the part, and the organic layer 303 which is stacked on the transparent electrode 302 is formed so as to be thin. In the case where the film growth is performed by vapor deposition, particularly, when a convex part is formed by dust or the like, vapor deposition is hardly performed on side faces of the convex part, and hence the film growth is insufficiently performed.
In the thinned part of the organic layer 303, the distance between the cathode and the anode is shorter than that in another part, and therefore the current is easily concentrated to cause a problem in that the cathode and the anode are short-circuited. Even when such a defect does not result in a short circuit, the current for luminescence is concentrated into the thinned part of the grown film. As a result, the current hardly flows through the peripheral region of the part, thereby producing a problem in that the pixel fails to luminesce.
The invention has been conducted in view of the above-discussed problems. It is an object of the invention to provide a luminescent display in which a defect due to a short circuit between a transparent electrode and a metal electrode is repaired and the yield can be improved, and also a method of producing such a luminescent display.
According to a first aspect of the invention, in a luminescent display in which a first electrode, a luminescent portion, and a second electrode are sequentially stacked on a substrate, when a part of the luminescent portion is defective, only a part of the second electrode and corresponding to the defective part is removed away, a remaining part of the second electrode is left, and the defective luminescent pixel is enabled to luminesce by the first electrode and the remaining part of the second electrode.
According to a second aspect of the invention, in luminescent display in which plural first electrodes that are arranged at predetermined intervals, a luminescent portion, and plural second electrodes that are perpendicular to the first electrodes, and that are arranged at predetermined intervals are sequentially stacked on a substrate, a luminescent pixel is formed by using, as a unit, a region where one of the first electrodes and one of the second electrodes face and intersect with each other with interposing the region, and a predetermined number of such luminescent pixels are arranged in a matrix form, when an arbitrary one of the luminescent pixels which are arranged in a matrix form is defective, only a part of the second electrode and corresponding to the defective luminescent pixel is removed away, a remaining part of the second electrode is left, and the defective luminescent pixel is enabled to luminesce by the first electrode and the remaining part of the second electrode.
According to a third aspect of the invention, in the luminescent display of the second aspect of the invention, an organic electroluminescent element is used as the luminescent display.
According to a fourth aspect of the invention, in the luminescent display of the third aspect of the invention, the first electrodes are transparent electrodes, the luminescent portion is an organic layer configured by an organic electroluminescent element, and the second electrodes are metal electrodes.
According to a fifth aspect of the invention, in the luminescent display of the fourth aspect of the invention, the transparent electrodes, the organic layer, and the metal electrodes are sequentially stacked on a transparent substrate.
According to a sixth aspect of the invention, in the luminescent display of the fifth aspect of the invention, a protective film is formed on the transparent substrate on which the organic layer and the metal electrodes are formed.
According to a seventh aspect of the invention, in the luminescent display of any one of the second to fifth aspects of the invention, the luminescent display is driven by simple-matrix driving.
According to an eighth aspect of the invention, in a method of producing a luminescent display in which plural first electrodes that are arranged at predetermined intervals, a luminescent portion, and plural second electrodes that are perpendicular to the first electrodes, and that are arranged at predetermined intervals are sequentially stacked on a substrate, a luminescent pixel is formed by using, as a unit, a region where one of the first electrodes and one of the second electrodes and intersect with face each other with interposing the region, and a predetermined number of such luminescent pixels are arranged in a matrix form, the method comprises the steps of forming the first electrodes on the substrate; sequentially stacking the luminescent portion and the second electrodes; when an arbitrary one of the luminescent pixels which are arranged in a matrix form is defective, irradiating only a part of the second electrodes and corresponding to the defective luminescent pixel, with light; and removing away only the part which is irradiated with light.
According to a ninth aspect of the invention, in the method of producing a luminescent display of the eighth aspect of the invention, the substrate and the first electrodes are optically transparent, and the luminescent portion contains an organic compound.
In the invention configured as described above, even when a short circuit between the transparent electrode and the metal electrode, or the like occurs and a defective pixel such as a pixel which does not luminesce or a luminescence-defective pixel is formed, repairing is performed so as to remove only a part corresponding to the defective part, in the metal electrode corresponding to the region which corresponds to the defective pixel, and in which the transparent electrode and the metal electrode intersect with each other. Therefore, a current flow between the metal electrode and the transparent electrode which face each other via the organic layer is allowed by the remaining metal electrode, thereby enabling the pixel and the subsequently scanned pixels to luminesce.
According to this configuration, it is possible to design a luminescent display which can be sufficiently put into a practical use even when the display has few defective pixels, thereby contributing to an improved yield due to repairing of defects.